This invention relates to a printing apparatus equipped with a loading mechanism for loading and unloading inksheet cassette from the printing apparatus. More particularly but not exclusively. it relates to a thermal transfer printer of the so-called shell type which is equipped with such a loading mechanism.
FIG. 1 is a schematic profile of a conventional shell-type thermal transfer printer of the type to which the present invention relates. As shown in the figure, a shell-type printer has a box-like base 1 and a cover 3 which is pivotably supported by pins 2 which are secured to the rear end of the base 1. The base 1 has a thermal print head 5 mounted therein, while the cover 3 supports a platen 6 and pinch rollers 7a and 7b which are disposed on either side of the platen 6. A paper supply cassette 8 for recording paper and a paper discharge tray 9 are secured to the cover 3. The base 1 houses a removable inksheet cassette 10, the structure of which is shown in detail in FIG. 2. The inksheet cassette 10 has a 4-sided cassette case 14 whose top and bottom are open. A supply roller 11 and a take-up roller are rotatably mounted inside the case 14, and an inksheet 13 is wrapped around these rollers. Two pairs of studs 15 and 16 project outwards from opposite sides of the case 14. These studs 15 and 16 fit into corresponding notches formed in two pairs of positioning plates 17 and 18 which are secured to the base 1 on opposite sides thereof.
The thermal print head 5 and the platen 6 are respectively secured to the base 1 and the cover 3 so that when the cover 3 is closed, the platen 6 will confront the print head 5 in close proximity thereto. Furthermore, the positioning plates 17 and 18 are positioned such that when an inksheet cassette 10 is mounted thereon and the cover 3 is closed the inksheet 13 of the cassette 10 will lie between the print head 5 and the platen 6. During printing, as illustrated in FIG. 3, recording paper 19 is supplied from the paper supply cassette 8 and passes through the space between the inksheet 13 and the platen 6. At the same time, the inksheet 13 is transferred from the supply roller 11 to the take-up roller 12 in the direction shown by the arrows in the figure.
In a conventional shell-type printer of this type, the inksheet cassette 10 must be loaded into the base 1 of the printer entirely by hand. As shown in FIG. 1, the inksheet cassette 10 must be lowered into the base 1 from above by hand until the studs 15 and 16 fit into the notches in the positioning plates 17 and 18. The process of inserting the cassette 10 into the base 1 and guiding it by eye onto the positioning plates 17 and 18 is made difficult by the fact that the cover 3 can be opened by only a relatively small angle with respect to the base 1. Because of the limited space between the top of the base 1 an the cover 3, during loading or unloading of the cassette 10, it is easy to inadvertently strike it against one of the fragile parts of the printer, such as the thermal head 5, thereby damaging the printer.
With other types of printers, it is conceivable to insert an inksheet cassette horizontally into the base while guiding the cassette with guide rails or other type of guide mechanism. However, with a shell-type printer, due to the position of the thermal head, it is mandatory that an inksheet cassette be inserted from above, and therefore simple guide rails are difficult to adapt to a printer of this type.